Preparation of thermoset cycloolefin polymers via metathesis catalysts is a relatively recent development in the polymer art. Klosiewicz, in U.S. Pat. Nos. 4,400,340 and 4,520,181, teaches preparation of such polymers from dicyclopentadiene and other similar cycloolefins via a two-stream reaction injection molding technique wherein a first stream, including the catalyst, and a second stream, including a catalyst activator, are combined in a mix head and immediately injected into a mold where, within a matter of seconds, polymerization and molding to a permanently fixed shape take place simultaneously.
In the typical system, according to Klosiewicz, the catalyst component is a tungsten or molybdenum halide and the activator is an alkyl aluminum compound. Most strained ring non-conjugated polycyclic cycloolefins are metathesis polymerizable. These include, for example, dicyclopentadiene, higher order cyclopentadiene oligomers, norbornene, norbornadiene, 4-alkylidene norbornenes, dimethanooctahydronaphthalene, dimethanohexahydronaphthalene and substituted derivatives of these compounds. The preferred cyclic olefin monomer is dicyclopentadiene or a mixture of dicyclopentadiene with other strained ring hydrocarbons in ratios of 1 to 99 mole % of either monomer, preferably about 75 to 99 mole % dicyclopentadiene.
The metathesis catalyst system is comprised of two parts, i.e., a catalyst component and an activator. The preferred catalyst component as taught by Klosiewicz has been a tungsten halide, and preferably a mixture or complex of tungsten hexachloride (WCl.sub.6) and tungsten oxytetrachloride (WOCl.sub.4).
The tungsten or molybdenum compound of Klosiewicz is not normally soluble in the cycloolefin, but can be solubilized by complexing it with a phenolic compound.
In U.S. application Ser. No. (315,075, filed Feb. 24, 1989, now U.S. Pat. No. 4,981,931) by Bell, was disclosed tungsten catalyst compositions for metathesis polymerization comprising ##STR1## where X is Cl or Br, n is 2 or 3, R.sup.1 is a H, a Cl, an alkyl group having 1-10 carbons, an alkoxy group having 1 to 8 carbons, or a phenyl group, R.sup.2 is H or an alkyl group having 1 to 9 carbon atoms and R.sup.3 is a H or an alkyl group having 1 to 10 carbon atoms for use with a trialkyltin hydride or a triphenyltin hydride activator. A process to employ such tin activator compounds in a system in which gelation and polymerization were delayed for at least a time sufficient to charge the reaction mixture to a mold. Both the catalyst and activator compounds had improved stability, with resistance to oxygen and moisture. The catalyst compounds were easy to isolate, instead of being mixtures as are those found in the prior art. Although certain advantages were found, these compounds when used to polymerize strained ring cycloolefins produced polymers with a higher than desired residual monomer level.
It is therefore an object of this invention to provide a catalyst composition that polymerizes strained ring polycyclic cycloolefins that have very low levels of residual monomer.
There is also a need for polymers of the type described by Klosiewicz to have higher levels of heat resistance, while maintaining other properties, such as impact and tensile strengths at levels similar to those found in prior art strained ring cycloolefin polymers. Previously, improved heat resistance was obtained through use of comonomers with the dicyclopentadiene (DCPD) monomer. The improved heat resistance was previously obtained at the cost of decreased impact resistance. Therefore it is a further object of this invention to provide catalyst compositions that polymerize strained ring polycyclic cycloolefins producing polymers with a higher level of heat resistance than prior art polymers while maintaining their impact strength.
Another object of this invention is to find catalysts that are more efficient in polymerizing dicyclopentadiene.
This invention is a process for preparing a polymer which comprises contacting a strained ring polycyclic polyolefin with a substantially pure tungsten complex, having the formula WOCl.sub.4-x (OAr).sub.x wherein OAr represents a mono-, di-, tri-, tetra- or penta- substituted phenoxy group and where x is 1, 2 or 3. These catalysts are efficient and promote catalysis of dicyclopentadiene at catalyst concentration levels of 1 part catalyst to 4000 parts monomer or less.
Various activator compounds may be employed as are known in the art to act together with the tungsten catalyst complexes described above to cause the polymerization of strained ring polycyclic cycloolefins. Among the activator compounds that can be employed in the practice of this invention are trialkyltin hydrides, triaryltin hydrides, diethylaluminum chloride, diethylzinc, dibutylzinc, and triethylsilane. Mixtures of two or more activator compounds may produce more desirable polymerization conditions and more desirable polymer properties than a single activator compound in certain situations.
Of the trialkyl tin hydrides, suitable for use in the process of the invention, tri-n-butyltin hydride is preferred. Among the triaryltinhydrides is triphenyltin hydride.
As stated already hereinbefore the DCPD monomer used herein was of highly pure grade, containing less than 2% impurities. The DCPD used in the following examples was about 98-99% pure monomer. Other monomers or comonomers employed in the practice of this invention should also be of about this degree of purity. However, it is also contemplated that the polymerization feed compositions of this invention can polymerize less pure grades of dicyclopentadiene when the appropriate tungsten catalyst compound, activator compound and other components are employed.
When the two parts of the catalyst system, the tungsten catalyst and the tin activator, are combined, the resulting cycloolefin (for example, DCPD) to catalyst compound ratio will be from about 500:1 to about 15,000:1 on a molar basis, preferably 2000:1 and the molar ratio of the tungsten complex versus the tin activator compound will be from about 1:2 to 1:6.
Generally the polymerization takes place in bulk, but the catalyst components may be dissolved in a small amount of solvent, such as toluene. It is preferred, however, to use DCPD as a solvent. When the liquid tri-n-butyltin hydride activator compound is used, no solvent is necessary for its addition and triphenyltin hydride is readily soluble in DCPD.
A preferred method in the practice of this invention for the polymerization of DCPD is to contact a tungsten compound catalyst component stream with a tin compound activator component stream wherein at least one of the streams contains the DCPD. For example, it is possible to dissolve the tungsten catalyst in DCPD and either to dissolve the activator in DCPD or in another solvent or to use the activator without any solvent. Usually both the tungsten catalyst and the tin activator are first dissolved in separate streams of DCPD prior to the mixture of said streams.
After the streams have contacted with each other the resulting mixture may be injected or poured into a mold, where the polymerization takes place. The polymerization is exothermic, but heating the mold from about 50.degree. to 100.degree. C. is preferred.
The tungsten catalyst may be stored in DCPD for some time, provided that the DCPD contains only a few ppm of water or less. The tin activator compounds are storable in DCPD for prolonged periods and tolerate relatively higher levels of water than the catalysts without losing their activity. During the polymerization of DCPD various additives can be included in the reaction mixture to modify the properties of the polymer product of the invention. Possible additives include fillers, pigments, antioxidants, light stabilizers, plasticizers and polymeric modifiers.
The invention further relates to a two component catalyst system, comprising
(a) a tungsten compound of the formula WOCl.sub.4-x (OAr).sub.x wherein Ar represents a hindered phenyl ring substituted with bulky alkyl groups containing 1-10 carbon atoms, alkyl ketone or ester groups, carboxyl groups, alkoxyl groups, halogens or aryl groups, i.e., diisopropyl or phenyl groups, represented by R below and x=1, 2 or 3. Among the preferred molecules or groups that are substituted on the phenyl ring include chlorine, bromine, iodine, phenyl, methoxy, CHO, COOCH.sub.3, COR' (where R' is any of the groups that can be substituted on the phenyl ring as represented by R) and isopropyl. The substituents need not be identical on a particular phenyl ring. For example, a trisubstituted phenyl group such as 2,4-dichloro-6-methyl phenyl. A generalized formula to take the case of the mixed substituents into consideration is, e.g., WOCl.sub.p (OAr).sub.q (OAr).sub.r where p+q+r=4 Monodi, tetra, and penta substituted phenols can also be employed in making the tungsten compounds employed in this invention. The desired tungsten compounds are prepared by reacting the appropriate phenol with WOCl.sub.4 in solution. The molar ratio of phenol to WOCl.sub.4 is about equal to x in the generalized formula WOCl.sub.4-x (OAr).sub.x. The invention is also contemplated to include the use of mixtures of two or more different tungsten compounds. The phenyl ring, symbolized by Ar in the above general formula may have R substituted at the 2,3, or 4 positions. In the disubstituted phenyl ring the substituents R.sub.1 and R may be at the 2,6; 2,5; 2,4 or 2,3 positions or at the 3,2; 3,4; 3,5 or 3,6 positions. R and R.sub.1 may be the same or different groups. In the trisubstituted phenyl ring substituents R, R.sub.1 and R.sub.2 may be at the 1,3,5; 2,3,4; or the 3,4,5 positions, where R, R.sub.1 and R.sub.2 may be the same or different. The two tetra substituted structures for the phenyl ring have substituents at the 2,3,5,6 or the 2,3,4,5 positions, where R, R.sub.1, R.sub.2 and R.sub.3 may be the same or different. An example of such would be made from 2,3,5,6-tetrachlorophenol. The penta substituted ring has substituents at the 2,3,4,5 and 6 positions, where each substituent may be the same or different. An example of the penta substituted structure would be made from C.sub.6 F.sub.5 OH. and
(b) an activator compound that is triphenyltin hydride or trialkyltin hydride such as a tributyltin hydride. The phenyl group of the tungsten compound may have other substituents. Alkyl and phenyl zinc compounds, triethylsilane (in combination with a trialkytin hydride, alkylaluminum compounds, alkylalkoxyaluminum halides and dialkylaluminum halides may also be employed.
In order to maintain the stability of tungsten compounds of the present invention with the 98-99% dicyclopentadiene without premature gelation, it is usually necessary to add a stabilizer compound to the solution containing the tungsten compound, and a rate moderator to the solution containing the tin activator compound. It is preferred to store the tungsten compounds in solution in dicyclopentadiene. When the stabilizer compound is omitted, a slow polymerization of the monomer proceeds in the storage container. Stabilizer compounds include diethylether (OEt.sub.2); ethyleneglycoldimethylethers (glyme), bis(methoxy)ethylether (diglyme), benzonitrile, acetonitrile, tetrahydrofuran, bulky phenols (such as 2,6-di-t-butyl-4-methyl phenol (BHT)), bisphenols such as 4,4'-methylenebis(2,6-dimethylphenol) (sold under the tradename Lowinox 44M26), or 2,2'-methylene(4-methyl-6-t-butyl phenol) (sold under the tradename Vulkanox BKF) or polyphenols such as 1,3,5-trimethyl-2,4-6-tris(3,5-di-t-butyl-4-hydroxybenzene) benzene (sold under the tradename Ethanox 330) may also be used. In addition, mixtures of the above stabilizer compounds such as a mixture of diglyme and one or more phenols or other Lewis bases can be employed in the practice of this invention. The stabilizer compound prevents such polymerization from occurring until the addition of the activator compound. The rate moderator compound prevents the polymerization process from being too rapid, provides for adequate mixing of the catalyst components, and allows the mold to be completely filled. The rate moderator compounds include various nitrogen or phosphorus compounds used for this purpose as described in U.S. Pat. Nos. 4,727,125; 4,883,849; and 4,933,402. Preferred rate moderators include pyridine (py); pyrazine (pyz); tributylphosphine (Bu.sub.3 P); tributylphosphite (TBP); triisopropylphosphite (TIPP); 2,6-dimethylpyrazine (Me.sub.2 pyz). The more preferred rate moderators are phosphines and phosphites, e.g., tributylphosphine (PBu.sub.3) and tributylphosphite ((BuO).sub.3 P). The stabilizer and rate moderator compounds are not necessary when lower purity dicyclopentadiene is employed, unless prolonged storage times are desired. Also, the stabilizer is not necessary when prolonged storage of the catalyst in the monomer is not desired.
In some embodiments of this invention, a preformed elastomer which is soluble in the reactant streams is added to the metathesis-catalyst system in order to increase the impact strength of the polymer. The elastomer is dissolved in either or both of the reactant streams in an amount from about 3 to about 15 weight percent range, based on the weight of monomer. Illustrative elastomers include natural rubber, butyl rubber, polyisoprene, polybutadiene, polyisobutylene, ethylenepropylene copolymer, styrene-butadiene-styrene triblock rubber, random styrene-butadiene rubber, styrene-isoprene-styrene triblock rubber, ethylene-propylene-diene terpolymers, ethylene vinylacetate, and nitrile rubbers. Various polar elastomers can also be employed. The amount of elastomer used is determined by its molecular weight and is limited by the viscosity of the resultant reactant streams. The resultant reactant streams containing elastomer cannot be so viscous that mixing is not possible. Although the elastomer can be dissolved in either one or both of the streams, it is desirable that it be dissolved in both.
In addition to measuring gel and cure times and residual DCPD monomer level, a measurement of swell value was made. The swell value is an indication of the degree of crosslinking in the polymer, i.e., lower swell values indicate higher degree of crosslinking. The general procedure used for swell value determinations is as follows: A 5 gram sample of polymer is removed from its test tube (by breaking the glass) and carefully sliced into 1-2 mm thick sections across the cylindrical axis with a tile cutter. The burrs are removed, each slice weighed to the nearest milligram and strung onto a stainless steel or copper wire taking care to keep them in known sequence. This is done for each sample at a given monomer feed. The wire is made into a closed loop and placed in 50 ml of toluene for each gram of polymer. These flasks are then heated to reflux for 16 hours (overnight) and cooled. Each loop is successively removed from the flask and placed in a small dish of fresh toluene. The slices are removed, patted dry, and weighed individually, again taking care not to disturb their sequence or to tear the swollen samples. The swell values are calculated using the following formula: swell (%)=(w.sub.2 -w.sub.1)/w.sub.1 .times.100%, where w.sub.1 =initial weight of polyDCPD sample and w.sub.2 =weight of solvent swollen polyDCPD sample. Since the swell value is an indication of the degree of crosslinking in the polymer, low values are preferred.
The best mode now contemplated of carrying out this invention will be illustrated with the following examples. The examples are given for the purpose of illustration only and the invention is not to be regarded as limited to any of the specific materials or conditions used in the examples.
In the following examples, in which tungsten complex catalyst components are prepared, tungsten hexachloride (WCl.sub.6) was obtained from GTE Sylvania Chemical Company and used as received. 2,6-diisopropylphenol and 2,6-dichlorophenol (HOC.sub.6 H.sub.3 -2,6-Cl.sub.2) were purchased from Aldrich Chemical Company and used as received. Hexamethyldisiloxane (Me.sub.3 SiOSiMe.sub.3) (Aldrich) was sparged with dry nitrogen before use.
Cyclopentane, diethyl ether, and pentane were dried over 4A molecular sieves and sparged with nitrogen prior to use. Toluene was placed in contact with 13X molecular sieves and sparged with dry nitrogen before use.
All operations were carried out under a dry nitrogen atmosphere or in vacuum either in a Vacuum Atmospheres Dri-Lab (inerted by argon gas) or using Schlenk techniques. All solvent transfers must be performed by cannula or syringe techniques to maintain an inert atmosphere.
In the Examples in which polymerization studies are set forth, the following general procedures were followed. All manipulations were performed anaerobically in nitrogen-sparged pop bottles or under an argon atmosphere (Vacuum Atmospheres Dri-Lab) or using Schlenk techniques. Tri-n-butyltin hydride (packaged in Sure/Seal bottle) was purchased from Aldrich Chemical Company and stored refrigerated (0.degree. C.). Diglyme was dried by placing it over 3A molecular sieves and sparged with nitrogen before use. Where necessary rate moderators, such as tributylphosphite (Albright and Wilson), were dried over molecular sieves and sparged with dry nitrogen prior to use.
Polymerizations were conducted in nitrogen-sparged test tubes by adding together the catalyst and activator components (2.5 ml of each), mixing on a vortex mixer and then inserting the tube into an oil bath at 80.degree. C. or higher or into a heated block at about 33.degree. C. Gel times were estimated by observing the initial viscosity change and the times were taken when the polymerization raise the exotherm to 100.degree. C. or 180.degree. C., and to the maximum temperature of the polymerization. Polymer swells were obtained by refluxing the samples in toluene for 16 hours, cooling for four hours and determining the percentage weight gain.
The tungsten starting material used in all catalyst preparation is tungsten oxytetrachloride complex (WOCl.sub.4). This compound was prepared in the following manner. A solution of hexamethyldisiloxane (HMDS) (13.40 ml, 0.063 mol) in toluene (100 ml) was added dropwise into a toluene (200 ml) solution of WCl.sub.6 (25 g; 0.063 mol) in a 500 ml round bottomed flask (with stirring) over a 75 minute period. After the HMDS addition was completed, the column was removed and the reaction mixture was allowed to stir overnight under nitrogen. The brown solution was filtered in the dry box to yield a quantity of crude, orange WOCl.sub.4 (19.02 g; 88% yield). Immediately before use, the crude material was sublimed under reduced pressure at 100.degree. C. in small portions to give bright orange crystalline WOCl.sub.4. Pure commercial quantities of WOCl.sub.4 may be substituted in any of the catalyst preparations.